Virgin Islanders can become part of the citizen science movement this month when from Oct. 1 through 15, community members can join in the Great Virgin Islands Frog Count.
“Basically, we are asking the community to go outside and take audio recordings from their location, and we’ll map that location and put whatever frogs are heard in the recordings on the map,” said wildlife biologist Renata Platenberg. “We can use that information to look at frog species distribution patterns, frog communities, presence/absence of non-natives, patterns related to urbanization, etc.”
For now, Platenberg is asking people to send her their recordings and location data by email. Details are online at the Great Virgin Islands Frog Count website.
Frogs are creatures which love heavy rain events, and many of them have thrived since hurricanes Irma and Maria thrashed the territory in 2017.
Unfortunately, two invasive species of frogs – Cuban tree frogs and cane toads – have done especially well since the storms by taking advantage of pooling water and preying on the much smaller native frogs. The Puerto Rican coqui, which is also not native to the Virgin Islands, is also flourishing.
“Three of the four species of natives are known as rain frogs,” Platenberg said. “They live in seasonal dry forests and have adapted to surviving and reproducing in habitats without standing water.”
With few ponds or rivers available year round in the Virgin Islands, native rain frogs have evolved to lay their eggs in trees.
“One parent typically remains with the eggs and keeps them moist by soaking up water and transmitting it through its skin to the eggs,” Platenberg said. “These frogs are silent during the dry season – typically January ’til May – but when the spring rains come and the habitat becomes moist, they start reproducing.”
Their symphony of clicks, tocks, chirps and tweets fills the tropical nights.
Each species of frog prefers a different place to lay their eggs. Whistling frogs, which are the size of a finger nail, lay their eggs in bromeliads. Coquis, which are about half the size of a finger, lay their eggs on leaves and in tree cavities. Ditch frogs make little foam nests underneath rocks or logs near guts; their tadpoles hatch in the foam and remain there until it rains and they can safely emerge.
The small native frogs can live for a couple of years if they’re not eaten by something bigger. The bigger Cuban tree frogs can live for five years, and cane toads can live even longer.
Male and female Cuban tree frogs are different sizes, according to Platenberg. The males are the size of a thumb, but the females are much larger – the size of a palm of the hand. They will eat lizards, scorpions, grasshoppers, native frogs and even each other.
Cuban tree frogs can be recognized by their raucous, grating calls. They migrate to sources of water to breed, so standing water left by tropical storms works to their advantage. They’ve been known to enter cisterns through unscreened downspouts or overflow ports, and their calls magnified in the cavernous space can drive homeowners mad.
“They’re really hard to get out of cisterns,” Platenberg said. “Some desperate people drain their cisterns to get rid of them.”
Both invasive species are poisonous. Cuban tree frogs produce a sticky, stinky mucus that causes blisters, especially if it gets in a person’s mouth or eyes. These frogs are not fatal if ingested, and their mucus is less dangerous if it simply gets on the skin.
Cane toads are much more toxic than Cuban tree frogs, Platenberg said.
“They have a toxin that is secreted through their skin glands when they are threatened, and more specifically, if they are picked up and squeezed, as they would be by a potential predator,” Platenberg said. “They are seriously bad news to pets, and more than a few dogs have died on St. Croix where there are more ponds that support Cuban tree frogs and cane toads.
If you see a dog bite a cane toad, flush out its mouth and take the dog to the veterinarian,” she said.
Other stories in the “Two Years Post-Irmaria” series are: